Trophectoderm is the first epithelium of the mammalian preimplantation embryo and it develops into placental tissue which is essential for normal implantation of the embryo into the uterine lining. Evidence is provided to show that specific cytoskeletal elements, present in the eggs and embryo cells of a mammal, can be utilized as stage-specific markers for critical developmental changes during trophectoderm formation. It is proposed that these cytoskeletal elements be characterized at the molecular level for comparison to known cytoskeletal proteins. In addition, these specific elements will be analyzed for normal structure and function under experimental conditions in which the embryos and culture environments are manipulated to purturb ion transport, cell surfaces, cytoskeletal integrity, junctional associations between embryo cells and endocrine parameters. Defined extraction and purification procedures will be used to obtain the cytoskeletal material, and biochemical analysis will include protein electrophoresis, polypeptide finger-printing and RNA extraction and characterization. Ultrastructural analyses will be performed with extracted embryonic cytoskeletons as embedment-free sections. Because these specific cytoskeletal elements exhibit a developmental pattern of structural change, reorganization and finally disappearance from differentiated trophectoderm cells, the proposed approaches will provide new information about the role of the cytoskeleton in differentiation. The results of proposed manipulations will increase our knowledge of the requirements for normal embryo development and trophectoderm differentiation. The new information obtainable from the proposed research will provide insight into forms of human infertility related to abnormal early embryogenesis, and into improvement of procedures designed to produce normal human and domestic animal embryos in culture to improve reproductive success.